1. Field of the Invention
The present invention relates to a napped tricot pile fabric used for a vehicular upholstery which is knitted by applying a polypropyleneterephthalate fiber multifilament yarn to a ground yarn and a pile yarn and is finished by raising a sinker loop and by shearing napped fluffs to form a cut pile.
In the napped tricot pile fabric used for the vehicular upholstery, a polyethyleneterephthalate fiber multifilament yarn whose single fiber fineness is about 0.5˜6.0 dtex and whose total fineness is about 30˜180 dtex is applied generally to the ground yarn and the pile yarn. The density of the wale of the cut pile is more than about 30 W/25.4 mm. The density of the course of the cut pile is more than about 50 C/25.4 mm. The density of knit loop, which is defined by the product of the density of the wale of the cut pile and the density of the course of the cut pile, is about 1800˜2300 C×W/(25.4 mm)2.
2. Description of the Related Art
For preservation of natural resources and the global environment, renewable natural fibers such as cotton, linen, silk, wool, and the like are preferably used, because these fibers do not depend on non-renewable petroleum resources.
In this regard, a polypropyleneterephthalate fiber, called “PPT-fiber”, and a polylacticacid fiber are synthetic fibers that can be produced from natural plant fibers rather than from petroleum.
Japanese Patent Laid Open No. 2000-154457, Japanese Patent Laid Open No. 2002-004156, Japanese Patent Laid Open No. 2005-113279, and Japanese Patent Laid Open No. HEI-11-093050 disclose the PPT-fiber and the polylacticacid fiber that can be used for a vehicular upholstery fabric.
Since the vehicular upholstery fabric is used under severe conditions, a polyethyleneterephthalate fiber, called “PET-fiber”, is mainly used for the vehicular upholstery fabric. Natural fibers and rayon lack the durability of PET-fiber; thus, natural fibers and rayon are not desirably used for vehicular upholstery fabric.
In this regard, PPT-fibers and polylacticacid fibers are relatively new materials used for the vehicular upholstery fabric, since the chemical formula of polypropyleneterephthalate, known as “PPT”, and polylacticacid are similar to the chemical formulas of polyethyleneterephthalate, known as “PET”. However, polylacticacid fiber lacks corrosion resistance since it is a type of biodegradable fiber. Further, polylacticacid fiber lacks in the ability to absorb dyes.
Therefore, in the case of the application of polylacticacid fiber for use as a vehicular upholstery fabric, it must be chemically treated.
In this regard, in comparison with PET-fiber, the Young's Modulus of PPT-fiber is lower, the rate of elastic recovery of PPT-fiber is higher, and PPT-fiber is rich in flexibility and stretching property.
Thus, it is expected that vehicular upholstery fabric having an agreeable texture will be obtained by using PPT-fiber rather than PET-fiber.
However, when a napped tricot pile fabric is knitted from PPT-multifilament yarn rather than from PET-multifilament yarn, the cut-off-end-portion (where the fabric is cut off), does not remain straight but instead curls very easily.
Therefore, at the time of cutting and stacking of the napped tricot pile fabrics knitted from PPT-multifilament yarn, the curling of the cut-off-end-portion hinders the ability to stack the cut tricot pile fabrics by arranging the cut-off-end-portions in order. Further, at the time of sewing the cut tricot pile fabrics, in order to avoid the aforementioned curling problem, the cut-off-end-portion should be under tension by pulling from one side to the other side, or should be pushed down to prevent the cut-off-end-portion from curling. As a result, it takes a lot of time and labor to sew the cut tricot pile fabrics, and the tendency of the cut-off-end-portion to curl gives rise to inaccurate sewing which results in fabrics unusable for vehicle upholstery.
Therefore, using napped tricot pile fabric knitted from PPT-multifilament yarn (rather than from PET-multifilament yarn) for in vehicular upholstery has generally been avoided.
The cut-off-end-portion of the cut tricot pile fabric in which PPT-fibers had been used for the ground yarn and the pile yarn was minutely observed with regard to curling. Specifically, the following was observed:
(1) curling did not occur at the cut-off-end-portion where the napped tricot pile fabric is cut along the knitting length direction; but rather
(2) curling did occur at the cut-off-end-portion where the napped tricot pile fabric is cut along the knitting width direction crossing the knitting length direction. When PPT-multifilament yarn (rather than PET-multifilament yarn) is used to knit napped tricot pile fabric, the following should initially be considered:
(1) the needle loop and the sinker loop are formed by looping the ground yarn and the pile yarn in the knitting width direction;
(2) the ground yarn and the pile yarn in the napped tricot pile fabric are continuous in the knitting length direction:
(3) PPT-fiber is superior in stretching property (that is, the rate of elastic recovery) in comparison with PET-fiber which is conventionally used for the vehicular upholstery fabric;
(4) in comparison with PET-fiber, PPT-fiber shrinks more easily when heated;
(5) therefore, the shrinking stress caused from heating and corresponding with the tension which acts on the raw tricot fabric made from PPT-fiber during the knitting process is greater than that which acts on the raw tricot fabric made from PET-fiber during the knitting process;
(6) similarly, the heat shrinking stress which occurs and acts on the raw tricot fabric made from PPT-fiber during the dyeing and finishing process is greater than that which occurs and acts on the raw tricot fabric made from PET-fiber during the dyeing and finishing process;
(7) as a result, the potential stress which is stored up in PPT-fiber during the knitting and dyeing and finishing processes is realized as a shrinking stress for giving which gives rise to the curling in the knitting length direction, when the ground yarn and the pile yarn are extended during the cutting and sewing process and where tensile stress (tension) does not act on the fabric.
On further investigation, when PPT-multifilament yarn rather than PET-multifilament yarn is used to create napped tricot pile fabric, the following should be considered:
(1) the needle loop does not form a lanky-shape configuration elongated in the knitting length direction but instead forms a loop-like-shape configuration puffed in the knitting width direction, and even though the ground yarn and the pile yarn tend to shrink due to the potential stress stored in those fibers, the needle loop only turns into a loop-like-shape configuration as opposed to the usual lanky-shape configuration.
(2) the course intervals which are the size of a needle loop in the knitting length direction, hardly shorten;
(3) when the ground yarn and the pile yarn shrink, shrinkability of the napped tricot pile fabric in the knitting length direction is counteracted in accordance with the shrinking of the ground yarn (11) and the pile yarn (12); and
(4) as a result, the napped tricot pile fabric hardly curls in the knitting length direction.
On further investigation, when PPT-multifilament yarn rather than PET-multifilament yarn is used to create napped tricot pile fabric, the following should also be considered:
(1) when PPT-fiber used for the ground yarn is a bulky-texturized fiber which is bent finely and tortuously and has crimps, even though the PPT-fiber shrinks from the potential stress stored in it, only the crimps disappear and then the PPT-fiber is brought back to its original non-bulky texturized situation;
(2) then, if the crimps only disappear at the time PPT-bulky texturized fiber shrinks, then the course intervals hardly shorten;
(3) further, if the crimps only disappear at the time PPT-bulky texturized fiber shrinks, shrinkability of the napped tricot pile fabric in the knitting length direction is counteracted upon the shrinking of the ground yarn and the pile yarn;
(4) as a result, the napped tricot pile fabric hardly curls in the knitting length direction.
Upon additional investigation, when PPT-multifilament yarn rather than PET-multifilament yarn is used to create the napped tricot pile fabric, the following should also be considered:
(1) when the PPT-fiber is not made of only PPT (polypropyleneterephthalate), but instead is made of a combination of PPT and PET, polyethylentenephythalate (poly-ethleneterephth, which has a Young's Modulus higher than that of PPT and for which the rate of elastic recovery, flexibility and stretching property are lower than those of PPT), the potential stress of this PPT-PET conjugate fiber decreases in accordance with PET-component.
(2) therefore, in the case with this PPT-PET conjugate fiber, even though potential stress is stored within its fibers, the shrinking stress resulting from the potential stress is comparatively less (than with pure PPT fibers);
(3) as a result, the napped tricot pile fabric hardly curls in the knitting length direction even though the potential stress stored in the PPT-PET conjugate fiber is realized.
Upon further investigation, when PPT-multifilament yarn, rather than PET-multifilament yarn, is used to create the napped tricot pile fabric, the following should also be considered:
(1) when the pile yarn is a twist yarn, a strong raking stress is required during the raising process since the yarn is twisted and thus it is difficult to rake out the fibers of the pile yarn.
(2) during the raking process, a strong raking stress propagates from the sinker loop to the needle loop; that strong raking stress acts upon the pile yarn as a tensile stress;
(3) the tensile stress makes the needle loop strained in the knitting length direction, and the course intervals become shortened;
(4) the substantial length of the portion of the ground yarn of the needle loop thus becomes elongated compared to the substantial length of the portion of the pile yarn of the needle loop;
(5) accordingly the ground yarn becomes loose as a result of this elongation;
(6) thus, when the potential stress in the ground yarn is realized, the loosened portions of the ground yarn only recover their original form and original length:
(7) put another way, the course intervals shortened by the tensile stress which acts on the pile yarn during raising process are not shortened further by the potential stress which is realized in the ground yarn after the raising process; and
(8) as a result, even though the potential stress stored in the ground yarn is realized as a shrinking stress, shrinking caused by the shrinking stress in the knitting length direction of the napped tricot pile fabric is nonetheless counteracted, and, consequently, the napped tricot pile fabric hardly curls in the knitting length direction.